An organic EL display panel has a plurality of organic light-emitting elements arranged on a substrate. A light-emitting element has basically a pixel electrode, an organic light emitting layer and a counter electrode. In the organic light emitting layer, a hole and an electron form an electron-hole pair, and the pair acts as a light emitting exciter to make the organic light emitting layer emit light.
The light-emitting element contained in the organic EL display panel can be classified into a light-emitting element R emitting red light, a light-emitting element G emitting green light and a light-emitting element B emitting blue light. The element R, the element G and the element B in the organic EL display panel may have organic emitting layer emitting white light which is colored for each color by a color filter. On the other hand, the element R, the element G and the element B may have the organic light emitting layer emitting red light, the organic light emitting layer emitting green light and the organic light emitting layer emitting blue respectively. The light emitted from the organic light emitting layer is radiated to outside through the transparent electrode (the pixel electrode or the counter electrode). Since the light-extraction efficiency in the organic EL display panel is a few %, an improvement of the light-extraction efficiency is required.
In order to improve the light extraction efficiency, one of the pixel electrode or the counter electrode is made as a transparent electrode, and the other is made as a reflective electrode. This is to efficiently extract the emitted light from the organic light emitting layer from the transparent electrode. A part of the emitted light from the organic light emitting layer is directed to the transparent electrode; the other part of the light directed to the reflective electrode is reflected by the reflective electrode and directed to the transparent electrode. It is possible to improve the efficiency of the light extraction by preventing mutual damping of the light directed to the transparent electrode from the organic light emitting layer and the light reflected by the reflective electrode and directed to the transparent electrode.
A technology is reported for adjusting the optical distance from the organic emitting layer to the reflective electrode for preventing damping of the light to be extracted by arranging the transparent functional layer between the metal electrode which is the reflective electrode and the organic light emitting layer by sputtering or the like (refer to such as Patent Document 1).
In addition, a technology is known to adjust the film thickness of the transparent functional layer for each element to adjust the optical distance for each element (refer to Patent Documents 2 to 4). This is because in the organic EL display panel having the organic light emitting layer emitting red light, the organic light emitting layer emitting green light and the organic light emitting layer emitting blue light, the element R, element G and element B have different condition (the optical distance) for improving the light extraction efficiency.
In Patent Documents 2 to 4, the organic light emitting layer and the transparent functional layer for adjusting the optical distance are formed by sputtering, vapor-deposition technique, or the like.
A technology is also known to form the organic light emitting layer, the hole transport layer and the like by applying a solution containing the material of the organic light emitting layer and the hole transport layer and drying the solution. The area applied with the solution is defined by the separation wall (bank).
The shape profile of the functional layer formed with coating differs depending on the solute of the solution, kind of the solvent and their content ratio. For example, when each color filter film of the light-emitting element is formed with coating, the solute of the solution to be applied differs depending on color. For this reason, when the height and the taper angle of the separation wall (bank) are the same, the shape of the color filter film is liable to differ for each color. To cope with this problem, a technology is reported to change the height and the taper angle of the separation wall (bank) for each color of the color filter film for improving uniformity of the film thickness of the color filter film (refer to Patent Document 5, for example).
In addition, a technology is reported to make the shape of the pixel electrode concavely curved for improving uniformity of the film thickness of functional layer (refer to Patent Document 6 and Patent Document 7, for example).
Furthermore, a technology is reported to make the organic light emitting layer concavely curved for using efficiently the light emitted to the plane direction of the display (refer to Patent Document 8 and Patent Document 9, for example).